Bijay Kumar Show

Tribological Behavior of an Aluminum Matrix Composite with Al4SiC4 Reinforcement under Dry Sliding Condition

In the present research work, an aluminum-based metal matrix composite with in situ Al4SiC4 particles has been developed by the incorporation of TiC particles in commercial aluminum melt through a stir-casting method. Microstructure evaluation in correlation to developed hardness and mechanical properties was performed. Furthermore, the dry sliding wear behavior of commercial aluminum and commercial aluminum–5 vol% Al4SiC4 composite was investigated at low sliding speed (1 ms−1) against a hardened EN 31 disk at different loads. The wear mechanism involved adhesion and microcutting–abrasion at lower loads. On the other hand, at higher loads, abrasive wear involving microcutting along with adherent oxide formation was observed. The overall wear rate increased with load in the alloy as well as in the composite. Moreover, the overall wear rate of the composite was lower than that of the commercial aluminum at all applied loads.` The severe wear region at 39.2 N load in the case of the commercial aluminum–5 vol% Al4SiC4 composite was found to be delayed up to a longer sliding distance compared to commercial aluminum. The in situ Al4SiC4 particles offered resistance to adhesive wear. Accordingly, the commercial aluminum–5 vol% Al4SiC4 composite exhibited superior wear resistance compared to the commercial aluminum.

Accelerated lamellar disintegration in eutectoid steel

Abstract The fastest kinetics of lamellar disintegration (predicted duration of 44 min) in AISI 1080 steel is obtained with a novel approach of incomplete austenitisation-based cyclic heat treatment involving forced air cooling with an air flow rate of 8.7 m3 h−1. A physical model for process kinetics is proposed that involves lamellar fragmentation, lamellar thickening, divorced eutectoid growth and generation of new lamellar faults in remaining cementite lamellae in each cycle. Lamellar fragmentation is accentuated with faster rate of cooling through generation of more intense lamellar faults; but divorced eutectoid growth is ceased. Accordingly, as compared to still air cooling, much faster kinetics of lamellar disintegration is obtained by forced air cooling together with the generation of much smaller submicroscopic cementite particles (containing more proportion of plate-shaped non-spheroids) in divorced eutectoid region.

Tribological Behavior of a 0.33% C Dual-Phase Steel with Pre I/C Hardening and Tempering Treatment under Abrasive Wear Condition

ABSTRACT The present study investigates the effect of prior hardening and tempering treatment on the microstructure, mechanical properties, and high-stress abrasive wear response of 0.33% carbon dual-phase (DP) steel. For this purpose, two different DP steels were produced by subjecting the as-received steel to hardening (DP-H) and hardening + tempering (DP-HT) treatments prior to the intercritical (I/C) annealing treatment. These steels along with the as-received steel were subsequently characterized by optical and scanning electron microscopy (SEM) metallography. Furthermore, tensile properties were evaluated along with microhardness measurements. The fracture surfaces of the failed tensile specimens were studied under SEM. Prior hardening and tempering treatment resulted in the formation of a nearly spherical martensite (aspect ratio = 1.2 ± 0.13) phase along with fine iron carbides in DP-HT steel. These fine iron carbides and spherical martensite act as the void nucleation sites in DP-HT steel. Therefore, DP-HT steel exhibits good ductility along with reasonable strength. On contrary, DP-H steel exhibits the presence of a fine elongated martensite (aspect ratio = 6.1 ± 3) phase, which causes poor ductility. Furthermore, abrasion tests were carried out at varying sliding distances at three different applied loads. Dual-phase treatment results in improved overall wear response. Moreover, tempering of prior hardened steel leads to improvement in wear resistance in DP-HT steel under all conditions studied in comparison with DP-H steel. This is attributed to higher strain hardening and greater resistance to particle scooping in DP-HT steel.

Effect of prior austempering heat treatment on the microstructure, mechanical properties and high-stress abrasive wear behaviour of a 0·33% C dual-phase steel

The present study investigates the effect of prior austempering heat treatment on the microstructure, mechanical property and high-stress abrasive wear response of 0·33% carbon dual-phase (DP) steel. DP steels were produced by intercritical annealing of the as-received steel (DP-AR) and of the steel subjected to prior austempering heat treatment (DP-AT). Prior austempering heat treatment results in the refinement of martensite phase in DP-AT steel, which is responsible for generation of less strain and microcracks in the vicinity of martensite phases. Therefore, this steel exhibits improvement in ductility with a marginal loss in strength. On the other hand, DP-AR steel shows coarse martensite phase which promotes strain accumulation and thereby generation of microcracks. These microcracks are found to be responsible for poor ductility in this steel. Furthermore, abrasion tests were carried out at varying sliding distances at 7 N applied load. DP treatments result in improved overall wear response. However, prior austempering heat treatment results in improvement in wear resistance in DP-AT steel at all sliding distances except at initial period. This is attributed to finer morphology of martensite and the absence of microcracks along with higher strain hardening in DP-AT steel. However, the improved wear resistance at initial period of DP-AR steel is attributed to considerably higher strain hardening index at low strain as compared to DP-AT steel.

Wear Behavior of Cooling Slope Rheocast A356 Al Alloy

In the present study, the dry sliding wear behavior of rheocast A356 Al alloys, cast using a cooling slope, as well as gravity cast A356 Al alloy have been investigated at a low sliding speed of 1 ms−1, against a hardened EN 31 disk at different loads. The wear mechanism involves microcutting–abrasion and adhesion at lower load for all of the alloys studied in the present work. On the other hand, at higher load, mainly adhesive wear along with oxide formation is observed for gravity cast A356 Al alloy and rheocast A356 Al alloy, cast using a 45° slope angle. Unlike other alloys, 60° slope rheocast A356 Al alloy is found to undergo mainly abrasive wear at higher load. Accordingly, the rheocast sample, cast using a 60° cooling slope, exhibits a remarkably lower wear rate at higher load compared to gravity cast and 45° slope rheocast samples. This is attributed to the dominance of abrasive wear at higher load in the case of rheocast A356 Al alloy cast using a 60° slope. The presence of finer and more spherical primary Al grain morphology is found to resist adhesive wear in case of 60° cooling slope processed rheocast alloy and thereby delay the transition of the wear regime from normal wear to severe wear.